Use of radiation in extending the duration of host suitability for managing Ephestia kuehniella and Sitotroga cerealella by the egg parasitoid, Trichogramma evanescens

Full text: Laboratory studies were conducted to extend the duration of host suitability and to delay emergence of Trichogramma evanescens for managing Ephestia kuehniella and Sitotroga cerealella. Delaying emergence of Trichogramma spp. is critical for commercial parasitoid production. The effect of 3 months storage of irradiated eggs of E. kuehniella and S. cerealella on wasp quality was investigated. The hosts' eggs were less than 24 h old when they were irradiated with gamma radiation to prevent development. There was no significant difference on parasitisation, female and male emergence between gamma radiation doses and the untreated control up to 60 and 30 days for E. kuehniella and S. cerealella eggs, respectively. When the eggs were stored longer than these periods and then offered to T. evanescens females, no parasitisation was observed. Diapause induction was also considered for T. evanescens. It is a state of arrested development accompanied by physiological or somatic persistence. The effect of pre-storage temperature (3 deg. C, 7 deg. C, 10 deg. C, and 12 deg.. C) for 30 days and storage temperature of 3 deg C for 5 months, 70±5% R.H. and in full darkness was investigated for T. evanescens after parasitisation. Data obtained from diapaused T. evanescens stored at 3 deg. C for 20, 70, 100 and 150 days indicate that pre-storage temperatures affected the induction of diapause. It was possible to induce diapause in developmental stages of T. evanescens by exposing the pre-imaginal stages (prior to the prepupal stage) to 10 and 12 deg. C for 30 days. Adult emergence after long-term low temperature storage only occurred, when T. evanescens was in diapause. Parasitoids failed to enter diapause when prestorage temperatures were 3 and 7 deg. C for host eggs of both E. kuehniella and S. cerealella. Initial studies suggest that T. evanescens could be successfully stored at 3 deg. C. The long-term storage of host eggs and parasitoids in diapause allows an enlargement of the mass-rearing potentialities of this species for future biological control releases, by allowing procedures to stockpile the parasitoids for release at a suitable time. (author)